This invention relates to the field of potentiometers. More specifically, it relates to a wiper assembly for a potentiometer, of the type having a thick film or thin film resistive element.
Miniature rotary potentiometers typically employ a resistive element that is formed on a substrate in a substantially annular configuration, and concentrically surrounding a central conductive collector. Electrical contact is established between the collector and a selectable position on the resistive element by means of a contact mounted on a rotor. A common type of contact is that which is known as a "multi-wire wiper", comprising a multiplicity of individual wires, cantilever-mounted on the rotor in an abutting, side-by-side relationship, to form a multi-wire spring contact that brushes against, or "wipes", the resistive element as the rotor is turned. Examples of this type of contact are disclosed in the following U.S. Patents, all commonly assigned to the assignee of the present application: U.S. Pat. No. 3,704,436 to Froebe et al.; U.S. Pat. No. 4,186,483 to Laube et al.; U.S. Pat. No. 4,427,966 to Gratzinger et al.; and U.S. Pat. No. 4,810,994 to Froebe et al.
Multi-wire contacts exhibit low contact resistance and low contact resistance variation (CRV). Nevertheless, this type of contact still poses some problems, such as splaying or fanning of the individual wires, fragility and susceptibility to damage during handling and use, and side-to-side movement of the fingers ("chatter") while traveling over the resistive element. These problems have been ameliorated, but not altogether eliminated, by the use of bracing fingers, or "outriggers", on either side of the wiper element, which increases the manufacturing cost, while using some of the limited space available in such devices.
Another approach to the aforementioned problems is disclosed and claimed in U.S. Pat. No. 4,810,994 to Froebe et al. This patent relates to the use of a multi-wire wiper that is shaped as annular spiral. While excellent results have been obtained with the spiral-shaped contact assembly, improved performance is still desired, and further reductions in the size of the contact assembly, and the cost of manufacturing it, have been sought.